OBJECTIVES: Studies in amino acid and nitrogen metabolism of the fetus and newborn will include placental transport, ammonia production and utilization by placenta and fetus, and estimation of protein synthesis rate for specific fetal organs. 2. Studies in fetal carbohydrate metabolism will include placental lactate production under aerobic conditions, glucose turnover rate and rates of gluconeogenesis, and the effect of chronic fetal hyperinsulinemia upon glucose transport and utilization. 3. Studies on changes in distribution of fetal cardiac output and of cardiac output of the fetus and newborn during parturition will include cerebral and myocardial blood flow and the effects of acidosis, as distinct from hypoxia. 4. The role of estrogens and anti-estrogens and the quantitative description of tachyphylaxis in the uterine vascular bed will be studied in both pregnant and non-pregnant animals, including changes in mammary and uterine blood flow during parturition. 5. The role of glycoprotein synthesized by the trophoblast in immunosuppression, and thus in early trophoblast development, is being pursued through projects for purification of specific glycoprotein fractions having highest immunosuppressive activity. 6. Clinical studies describing the specific problems of markedly pre-term infants and the relationship of obstetrical factors in determining their outcome will include patent ductus arteriosus, echocardiography in the assessment of PDA, and an evaluation of the physiologic data most most useful in predicting the subsequent course of the newborn. 7. Studies on the relationship between fetal growth rate, placental size and placental pathology will include correlation between specific body proportions and placental size.